Birds and foot-and-mouth

Malcolm Ogilvie

Perhaps not
surprisingly, the possibility that birds might be carriers of foot-and-mouth
disease has been raised during the present epidemic, especially
recently when new cases have occurred many miles from existing ones
without, initially at least, any obvious animal, human or vehicle
connection. For example, a letter to the 'Scottish Farmer', a weekly
magazine widely-read among the farming community, warned of the
danger to cattle and sheep on the
islands of Bute and Islay when the Barnacle Geese wintering on the
Solway left for their arctic breeding grounds. However, the truth
of the matter is that this population of geese migrates north-east
to Svalbard (Spitsbergen), and so doesn't come anywhere near these
islands, which lie many miles to the north-west. And then 'The Times'
newspaper, reporting on the 30-mile leap of the disease from Dumfriesshire
to Jedburgh in the Borders, quoted an agricultural official as agreeing
that some of these same Solway geese could have fed on infected
grasslands on the Solway and then passed on the infection, presumably
through their droppings, as they flew over Jedburgh on their way
to their "Canadian" breeding grounds.

A third report
was even more improbable. A letter-writer to 'The Scotsman' newspaper
blamed birds of prey, saying that "the outbreaks appear most
prevalent where their numbers are excessive", which suggests
more than just a concern about foot-and-mouth, and suggested that
these birds, instead of being allowed to feed on diseased carcasses
and then roam freely, should be destroyed,. Fortunately a reply
was published pointing out that, of our British birds of prey, only
Golden Eagle, Sea Eagle and Red Kite were carrion feeders and that
the first-named was a very scarce breeder in south-west Scotland
(just two pairs in Dumfries and Galloway, plus one in Cumbria) and
that the other two were, at most, rare visitors. The writer added,
for good measure, that nowhere in Scotland were numbers of raptors
excessive and that, indeed, populations of some species were being
held down by illegal persecution.

So what is the
true state of affairs? Can birds transmit foot-and-mouth disease
and, more importantly, do they? In March, the RSPB commissioned
Professor Chris Feare, an independent agricultural scientist, to
investigate the matter. His report (which is available on the RSPB's
website, www.rspb.org.uk)
concluded that while there is a minimal, and theoretical, risk that
birds could spread the disease, there is no evidence from the scientific
literature or from a detailed analysis of earlier outbreaks in the
1950s and 1960s to suggest that they actually do. David Snow, who
anaalysed the 1967-68 outbreak, concluded that the spread of the
disease correlated best with the prevailing winds. Furthermore,
a large Starling roost near Oswestry in the area of the outbreak
had no detectable influence on the spread of the disease, which
actually by-passed the roost in its spread to the north-east and
never affected the farms in its immediate area.

One difference
from the 1967-68 outbreak is the presence, often for several days,
of dead animals left out in the open. Whether crows and large gulls,
which are undoubtedly feeding on these carcasses, could spread the
disease via their droppings is unknown, but is probably, again,
theoretically possible, but unlikely.

Dr
Ogilvie is a natural history writer and editor, formerly a research
scientist with the Wildfowl and Wetlands Trust, and resident
on the island of Islay since 1986. Until 1997, a member of the
'British Birds' editorial board and also one of the editorial
team which produced 'Birds of the Western Palearctic'.